Sub-miniature concentric tandem variable resistor and switch control



June 21, 1960 J. DI GIROLAMO 2,942,221

SUB-MINIATURE CONCENTRIC TANDEM VARIABLE RESISTOR AND SWITCH CONTROLFiled July 11, 1957 4 Sheets-Sheet 1 mm 27 e3 20 47 LVARIABLELMULTI-POSITION '1 RESISTOR SWITCH ON-OFF June 21, 1960 J, DI GIROLAMO2,942,221 SUB-MINIATURE CONCENTRIC TANDEM VARIABLE RESISTOR AND SWITCHCONTROL 4 Sheets-Sheet 2 Filed July 11, 1957 June 21, 1960 J. DIGIROLAMO 2,942,221

SUB-MINIATURE CONCENTRIC TANDEM VARIABLE RESISTOR AND SWITCH CONTROLFiled July 11, 1957 4 Sheets-Sheet s Jcsaph .Uwmlamc;

June 21, 1960 J. DI GIROLAMO 2,942,221

SUB-MINIATURE CONCENTRIC TANDEM VARIABLE RESISTOR AND SWITCH CONTROLFiled July 11, 1957 4 Sheets-Sheet 4 H 27 J59 hIhQzraZama sg ai g hgwUnited S ttes Patent SUB-MINIATURE CONCENTRIC TANDEM VARI- ABLE RESISTORAND SWITCH CONTROL Joseph Di Girolamo, Mishawaka, Ind., assignor to CTSCorporation, Elkhart, Ind., a corporation of Indiana Filed July 11,1957, Ser. No. 671,356

8 Claims. (Cl. 338-200) sufiicient size reduction in such concentrictandem controls, as to permit their use in the so-called transistoriz edradio receiving sets wherein transistors are used in place of the moreconventional tubes, and especially in transistorized automotive setswhere ruggedness is a primary consideration. Y

The extent to which this invention has attained its objective can bereadily appreciated from the fact that in one embodiment thereofcomprising a four-position tone control switch, a variable resistor andan on-olf switch, the overall size of the control is only ninesixteenths of an inch in diameter and three-fourths of an inch inlength.

Prior concentric tandem controls did not lend themselves to suchminiaturization because mere proportional reduction in the size of thecomponent parts thereof was limited by the need for maintaining adaquateelectrical clearance between grounded and live parts. Also, there is alimit to the extent shaft diameters may be reduced in a concentrictandem control, especially in automotive sets where ruggedness isrequired.

The crux of the problem resided in the fact that, with priorconstructions, the center connector of the variable resistor and, moreparticularly, the manner in which it was constructed and orientated withrespect to the resistance element, positively limited the size reductionwhich could be' effected. Accordingly, if the end sought by thisinvention was to be reached, an entirely new form of center connectorwould have to be devised. This has been done.

Another facet of this invention resides in the fact that j theindividual units of the complete control are'so constructed as toachieve an unprecedented flexiblity in assembly. Thus, with thisinvention, it is a simple matter to assemble into one combinationcontrol, two

individual variable resistors and an on-off switch; a multi- 4:

appear as the description proceeds, this invention resides in the novelconstruction, combination and arrangement of parts substantially ashereinafter described and more particularly defined by. the appendedclaims, it beingunderstood that such changes in the precise embodirnentof the hereindisclosed invention may be made as come within the scope ofthe claims.

; .'The accompanying drawings illustrate one complet example of' thephysical embodiment of this invention ponstructed according to the bestmode so far devised Patented JuneZl, 1960 ice for the practicalapplication of the principles thereof, and in which:

Figure 1 is a perspective view of a concentric tandem control embodyingthis invention, viewing the same essentially from the front;

Figure 2 is a longitudinal sectional view through the control shown inFigure l, and which, as is here clearly shown, comprises amulti-position switch, a variable resistor and an on-ofif switch;

Figure 3 is a perspective view of the control, viewing the same from therear but with the base of the on-off switch, which also serves as therear wall of the unit, removed and swung around to display the insideaspect thereof;

Figure 4 is a perspective view showing the rear of the fore part of thecontrol, with the variable resistor parts pulled off and swung around toshow the front thereof;

Figure 5 is an exploded perspective view of the multi position or tonecontrol switch viewing some of the parts thereof from the rear and theremainder thereof from the front;

Figure 6 is a perspective view of one of the component parts of themulti-position switch shown separated from the rest of the structure;

Figure 7 is a perspective view of the center connector or collector ringof the variable resistor, shown separated from the rest of thestructure;

Figure 8 is a perspective view of the stop washer which holds thecoaxial shafts against relative endwise displacement and also provides astop to limit rearward endwise movement of the rotors of the variableresistor and multiposition switch; and

Figure 9 is a longitudinal sectional view similar to Figure 2 butillustrating the composite control as com prising two variable resistorsand the on-off switch.

Referring particularly to the accompanying drawings and especially toFigure 2, it will be seen that the complete control of this invention iscontained within a housing structure built up of complementary parts,some of which are interchangable so as to give the control a desirableflexibility in assembly. This housing structure consists of two similartubular side wall forming members 10 and 11, each formed of insulatingmaterial, and both having the same inside and outside diameters andlength. Between the adjacent ends of these two tubular members is apartition wall 12 consisting of a disc of insulating material of adiameter slightly larger than that of the side wall forming members; andclosing the front and rear ends of the housing structure are'end walls13 and 14 each also formed by discs of insulating material slightlylarger in diameter than the tubular members.

These five parts, together with a spacing washer 15 overlying the frontwall 13 are held coaxially assembled by being confined between a metalground plate v16 which bears against the washer 15 and inturned fingers17 on the extremities of arms 18 extending rearwardly from the edge ofthe ground plate.

The arms 18 are received in aligned grooves 19 in th tubular side wallforming members and recesses 20 in the partition wall 12, the end walls13 and 14 and the spacer 15, so that the arms 13 not only serve to holdthe complementary housing parts in coaxial relationship, but also securethe same against relative rotation.

The ground plate 16 may have any suitable means provided thereon formounting the control upon a panel, as for instance, the three forwardlyprojecting ears 21 which have panel engaging shoulders 22 and narrowtangs 23 projecting therefrom, to enter appropriately located holesin'the mounting panel (not shown), where :they are secured by beingtwisted or bent over or by the solder dip fastening method.

ass-2,22 1

The partition wall 12 divides the interior of the housing structure intoaxially adjacent front and rear compartments, each of which is adaptedto contain at least one of the. individual units of the control. In thatembodiment of the invention illustrated in Figure 2, the frontcompartment contains a multi-position or tone control switch, indicatedgenerally by the numeral 24, and the rear compartment contains both avariable resistor, indicated generally by the numeral 25, and an on-offswitch 26. This combination of control units can be easily altered dueto the unusual interchangability of parts which this invention provides,and to illustrate th-ispoint, in the control shown in Figure 9 themulti-position tone control switch is supplanted by another variableresistor.

A characteristic of, this invention is that in the variable resistor aswell as the multi-position switch, the front Wall of the compartment inwhich the control unit is located provides the base for the statorportion of the unit. Thus, in. the control shown in Figure 2, thepantition wall 12 has; the arcuate resistance element 27 fixed to therear face thereof, and the front end wall 13 of the multi-positionswitchhas the stationary contacts 28, 29, 3t and 31, and the commoncontact 32 fixed on the rear face thereof. In the control shown inFigure 9, wherein the panel section or. unit of the control as well asthe rear unit is a v aniableresistor, the. front endwall 13', like thepartition wall, has an arcuate resistance element fixed thereon.

The; terminals 27' of the resistance element extend from theextremitiesthereof radially outwardly through notches 33 in the front end of thetubular side wall forming member 111,, and, the terminals 28', 29', 30,,31 and 32' ofthe, stationary switch contacts similarly project radiallyout. through notches 34 in the front end of the tubular side wall:forming member 10. The notches 33 and 34 are just deep enough and wideenough to accommodate the terminalsareceived.therein and, accordingly,the terminals will. be firmly held against any possible displacement.

The heads of the rivets by which the terminals 27' are secured to theinsulated base provided by the partition 12 (or the. front wall 13 whentwo resistors are mounted in tandem, as in Figure 9) with the ends ofthe resistance element 27 confined therebetween, project forwardlybeyondv the front of the base. By the same token, the heads of therivets by which the contacts 2341 and the ends of the tangs by which thecommon contact 32 are secured to the switch base, i.e. the front wall13, project forwardly of this base. in the case of the partition wall 12such forward projection of the rivet heads presents nov problem since,in this case, they merely extend into the front compartment but, in thecase of the front or panel unit, whether it be a variable resistor ormultiposition switch, the forwardly projecting rivet heads must'beaccommodated and held from contact with the ground plate. 16. This isthe function of the spacing washer 15 which is large enough to encircleand clear the adjacent forwardly projecting rivet heads and thick enoughto adequately space them from the ground plate.

As is conventional in concentric tandem controls, the rotor of the frontor panel unit is mounted on and driven by a tubular shaft 35, and therotor of the rear unit is mounted on and driven by a shaft 36 whichpasses through and is journalled in the tubular shaft. Preferably, theshaft 36 is solid and especially so in the present instance where theutmost size reduction is being sought. These coaxial shafts arerotatably supported by having the outer tubular shaft journalled inaligned holes 37 and 38, respectively, in the front end wall 13 and theground plate 16, and by having the rear end portion of thesolid innershaft journalled' in a hole 39 in the rear end-wall 14. The partitionwall 12 has a central aperture 40 through which the inner shaftprojects.

The rotor of the multi-position switch comprises a circular drive, arm41 molded of insulating material and having-a. forwardly. projecting hub42 and an eccentrioally disposed rearwardly projecting-stop lug 43. Thismolded drive arm is fixed to the rear end of the tubular shaft by meansincluding tangs 44 extending from the shaft and clinched over the rearface of the arm. A contactor 45 in the form of a ring stamped fromsuitable resilient metal is fixed on the front face of the circulardrive arm in a position encircling the hub 42. The securement iseffected by tangs 46 extending from diametrically opposite portions ofthe contactor and clinched around opposite notched portions of the drivearm. The unsecured portions of the contactor 45 are sprung forwardly andprovided with diametrically opposite fingers 47 and 48, the former beingadapted for'selective engagement with any one of the stationary contacts28 to 31, and the latter riding upon the common contact 32.

Detent action to hold the switch rotor in any one of its four positionsis provided by the engagement of the contact finger 48 into properlylocated holes 48 in the common contact.

The spring tension with which the contactor 45- engages the stationaryswitch contacts imposes a rearward axial thrust upon the tubular shaft35. This thrust is resisted and limited by the engagement of a C-shapedstop washer 49 having its bight portion received in a slot 50 in thetubular shaft and bearing against thefront face of the ground plate. Thebight of the C-shaped stop washer 49 also projects into an annulargroove 51 in the solid inner shaft 36 and thereby holds the shaftsagainst relative endwise displacement and also resists and limitsrearward axial displacement of the inner solid shaft.

The rotor of the variable resistor, like that of the multipositionswitch, comprises a molded circular drive arm 52 non-rotatably securedto the solidinner shaft 36 and provided with a forwardly projectingannular bead 53 and a rearwardly projecting eccentrically located stop1ug'54. Fixed to and overlying the front of this molded drive arm andencircling its forwardly projecting head 53, is; a ringlike contactor 55stamped of suitable resilient metal.

The contractor 55 has a fiat arcuate body portion. 56 with diametricallyopposite. tangs 57 extended from the opposite'outer edges thereof andclinched over opposite notched portions of the drive arm to secure thecontactor thereto with its body portion lying flat against the front ofthe drive arm. Arcuate spring contact fingers 58. ex.- tend from theends of they arcuate flat body portion 56 to overlie the drive arm.These spring contact fingers are substantially coplanar with. the bodyportion and are axially'biased forwardly towards the resistance. element27.v Their extremities are smoothly rounded and bear against theadjacent contact surface of the resistance element with. a forcedependent upon the stiffness of the spring fingers. The rearward thrustimposed upon the rotor as a result of this spring contact pressure isresisted and limited by the stop washer 49, as explained hereinbefore.

Although the spring tension of the fingers 5 8 resists forwarddisplacement of the rotor assembly of the vari able resistor, it isdesirable to provide a positive limit to the extent this spring tensionmay be increased by an accidental or unintentional pull on the shaft,and for this purpose, the annular bead 53 has a height such that in thenormal axial position of the rotor its edge is spaced just a shortdistance from the base (partition wall 12).

In the same manner, the hub 42 positively limits forward displacement ofthe rotor of the multi-position switch.

Bent back from its edge opposite that from which the contact fingers 58project and at points close to but be.-. tween the tangs 57, thecontactor has a pair of rearwardly directed parts 60 disposed at rightangles to the body portion 56. These parts 60 have spring contactfingers 61 extended therefrom toward one another and overlying theperiphery of the circular drive arm. The fingers 61 thus have widelyspaced anchored, ends provided by the parts 60, and closely spacedoutwardly biased free ends, theextremities of which are formed assmoothly rounded contacts 61 to engage the inside of a collector ring62.

The collector ring 62 difiers materially from the collector ringsordinarily used in variable resistors employed in radio and televisionreceivers, and because of this difference and the manner in which thespring fingers 61 of the contactor are arranged on the contactor totraverse the collector ring, an entirely unprecedented size reduction incontrols of this type has been made possible.

As best seen in Figure 7, the collector ring 62 is a sheet metalstamping rolled up into a ring of a size to be snugly received in acounterbore 63 in the tubular member 11. It is held therein with itsfront edge bearing against the shoulder provided by the bottom of thecounterbore, by a pair of diametrically opposite hold-down fingers 64extending rearwardly from the ring and bearing against the rear end wall14. A terminal 65 projects radially out from the rear edge of the ring62 through a notch 66 in the wall of the tubular member and, in sodoing, secures the ring against turning in the counterbore.

Since the ring is held against turning, it may be used to carry thestationary one of the cooperating stops by which the limits of rotaryadjustment of the variable resistor are defined. To this end, the ringhas a radially inwardly directed tongue 67 extended therefrom into thepath of the stop lug 54.

Attention is directed to the fact that the bottom of the counterbore 63which defines the position of the ring 62 in the tubular member, islocated about medially between the ends of the member 10. This assuressubstantial electrical clearance between the resistance element and thecollector ring.

The multi-position switch also has a stamped and rolled-up metal ring 70which .is quite similar to the ring 62, seated in a counterbore 63' inthe tubular member 10 and confined between the bottom of the counterboreand the partition wall 12 by diametrically opposite hold-down fingers 71extended from the rear edge of the ring. However, in this case, the ringhas no electrical function and serves only to limit rotation of theswitch rotor. For this purpose, the ring 70 has a pair of inwardlydirected stop lugs 72 formed thereon to lie in the path of the stopabutment 43 on the switch rotor, and an out-turned lug 73 which isreceived in a notch 74 in the wall of the tubular member 10 to hold thering 70 against turning.

The on-off switch 26, which as indicated hereinbefore is containedWithin the rear compartment along with the variable resistor, comprisesa stationary contact 75 fixed to and projecting forwardly from the rearend wall 14 and a resilient switch blade 76 anchored as at 77 to the endwall 14 and biased into engagement with the stationary contact, asclearly shown in Figure 3. The terminals 78 and 79 for the switchcomprise a rearward extension of the stationary contact 75 and a similarextension on the rivet 80 by which the blade 76 is anchored.

A cam 81 non-rotatably mounted upon the rear end of the solid shaft 36engages the switch blade to disen gage it from the stationary contactupon adjustment of the variable resistor rotor to one limit of itspermitted rotation.

From the foregoing description taken in connection with the accompanyingdrawings, it will be readily apparent to those skilled in the art thatthis invention has achieved an entirely unprecedented reduction in theoverall size of concentric tandem variable resistor-switch controls, andthat the key to this achievement resides in the novel reorganization ofthe parts of the variable resistor and, more especially, in the mannerin which the collector ring is disposed with respect to the rotor of thevariable resistor.

It will also be apparent that this invention has attained a newversatility in the combination of elements making up such concentrictandem controls, since the housing sections are substantially the samefor the variable resistor and the multi-position switch.

What is claimed asmy invention is: l. A concentric tandem radio andtelevision control of the type wherein a plurality of control units aredisa posed in concentric tandem relation and have rotors discsof-insulating material; a partition wall provided by a similar disc ofinsulating material, entirely separate from the side wall formingmembers, and clamped between the adjacent ends of the tubular members todi vide the housing structure into axially adjacent front and rearcompartments, eachof which contains one of the control units; a metalground plate overlying the disc forming the front end wall of thehousing structure; arms integral with the ground plate extendingrearwardly over the tubular members and said discs; and fingers on theextremities of said arms clinched over the disc which provides the rearend wall to thus hold the tubular members and said discs assembled andin coaxial relationship; the shafts passing through aligned holes in thedisc which provides the front end wall and in the ground plate, theouter shaft terminating inside the front compartment to drive the rotorof the control unit therein and the inner shaft projecting beyondtheouter shaft and through a hole in the partition wall into the rearcompartment to drive the rotor of the control unit therein.

2. The structure of claim 1 further characterized by the fact that therotor of each of the control units has a rotation limiting stop abutmentthereon to collide with a stationary stop abutment to define the limitsof rotation of the rotor, and characterized further by the fact thateach stationary stop abutment comprises a finger directed inwardly froma metal ring inserted into each tubular member from the rear end thereofand held against endwise displacement from a position at which saidfinger lies in the path of the stop abutment on the rotor, by beingconfined between a shoulder on the wall of the tubular member and thedisc at the rear end thereof, the ring being secured against turning bya finger projecting radially out from the ring and engaging in a recessin the tubular member.

3. The structure of claim 2 further characterized by the fact that eachtubular member is counterbored from its rear end, and by the fact thatthe ring is seated in the counterbore with its front edge bearingagainst the bottom thereof so that the bottom of the counterboreprovides said shoulder on the wall of the tubular member.

4. The structure of claim 2 further characterized by the fact that oneof said controls is a variable resistor comprising an arcuate resistanceelement having a fiat contact surface and a rotatable contactor having aspring contact finger to traverse said surface of the resistance elementand another spring contact finger to traverse a collector ring; thearcuate resistance element being mounted on the disc comprising thefront of the housing compartment in which the variable resistor islocated; and the contact finger which traverses the collector ring beingbiased radially outward into engagement with the inner surface of saidmetal ring so that said metal ring serves as the collector ring of thevariable resistor as well as a carrier for the stationary stop abutment.

5. The structure of claim 1 further characterized by the fact that thedisc closing the rear end of the housing structure has cooperatingstationary and movable switch contacts mounted on its inner face; andmeans to con trol engagement between said contacts formed on the rearend of the inner shaft which drives the rotor of the control in the rearcompartment.

6. As an article of manufacture, a contactor for the rotor of avariable, resistor comprising: a unitary sheet metal stamping having aflat body section; a pair of mounting ears at substantially oppositeside edges of the flat body section extending in the same directionperpendicularly to the plane of said section; a pair of resilientgenerally fiat contactor fingers extending from an edge of the bodysection at points near the mounting ears with said fingers projecting inthe same general direction from and substantially coplanar with the fiatbody section, said contact fingers being resiliently yieldable in adirection normal to the plane of the fiat body section and being biasedin the same direction out of said plane; and a second pair of resilientcontact fingers each having an anchored end portion provided by at partof the stamping which; is bent at right angles from an edge portion ofitsfiat body section, said second pair of contact fingers extending fromtheir respective anchored ends toward each other and having their freeends near one another, and said second pair of contact fingers beingresiliently yieldable in directions parallel to the plane of the flatbody section.

7. In a control of the character described: a housing for theinstrumentalities of the control including a cylindrical side wall ofinsulating material, said side wall being; counterbored from one endthereof and having a notch extending axially in from said end andopening to the counterbore; a metal ring seated in the counteubore withone edge thereof bearing. against the bottom of the counter-bore and itsother edge spaced inwardly of the open end of. the counterbore; an endwall across said end of the cylindrical side wall; a part on the metalring extending axially from its said other edge and engaged by the endwall so that the end wall holds the metal ring down against the bottomof the counterbore;v a lug projecting radially outwardly from said ringinto said notch to thereby hold the ring against turning with respect tothe side wall; a stop lug on the ring projecting radially inwardlythereof; a rotor constrained to rotation about an axis coaxial with thecylindrical side wall with a part thereof inside said cylindrical sideWall; and stop means on the rotor engageable with said stop lug todefine the limits of rotation of the rotor.

8. The structure of claim 7 wherein said control is a variable resistorand wherein said metal ring provides an. annular collector contact forthe resistor, and said radially outwardly projecting lug provides aterminal for said contact, and further characterized by the provision ofa resilient contact finger on the rotor resiliently hearing against theinner surface of said metal ring.

References Cited in the file of this patent UNITED STATES PATENTS1,572,645 Francesco Feb. 9, 1926 1,779,601 Kebler Oct. 28, 19302,506,491 De Boisblanc May 2, 1950 2,572,651 Mucher Oct. 23, 19512,712,583 Mucher July 5, 1955 2,789,191 Arisman et al Apr. 16, 1957

